1. Field of the Invention
The present invention relates to a display device, and more particularly to a display device which can obviate drawbacks such as disconnection of a connection portion or a printed circuit board for bridging caused by elongation and shrinkage of a multi-layered printed circuit board which supplies signals for display transmitted from a signal source side to leads for supplying signals for display to a large number of respective electrodes formed on an inner surface of an insulating substrate.
2. Description of the Related Art
Recently, as display means of information equipment such as a personal computer or a television set, a so-called flat-panel-type display device has been popularly used. As this type of flat-panel-type display device, a display device using a liquid crystal panel, a plasma panel and an organic EL panel have been widely known. Although these display devices are classified into several types depending on pixel selection methods, the active matrix method which performs the selection of pixels using active elements such as thin film transistors constitutes the main stream.
The flat-panel-type display device includes an insulating substrate on which active elements are formed and pixel forming elements are provided between pixel electrodes which are driven by the selected active elements and another electrodes. The insulating substrate is usually formed of a glass plate or a ceramic plate. As the flat-panel-type display device, a display device which uses a liquid crystal panel which changes orientations of molecules of liquid crystal present between the above-mentioned pixel electrodes and another electrodes constitutes a typical example. Further, in the display device which uses a plasma panel, a plasma discharge is generated between pixel electrodes driven by selected active elements and another electrodes and ultraviolet rays generated by the plasma discharge are subjected to the wavelength conversion by fluorescent materials formed on another substrate.
Then, the display device which uses the organic EL panel sandwiches light emitting layers made of an organic material between pixel electrodes and other electrodes and generates visible images by making use of a so-called electric field light-emitting phenomenon. Respective flat-panel-type display devices of these types adopt substantially the same mechanism for selection of pixels and hence, the explanation is made by taking the active-matrix type liquid crystal display device using thin film transistors as active elements as an example. That is, the present invention is not limited to such a liquid crystal display device and is applicable to the above-mentioned other flat-panel-type display devices.
The active-matrix type liquid crystal display device (hereinafter, simply referred to as “liquid crystal display device”) includes a plurality of groups of first electrodes (hereinafter also referred to as “scanning lines”, “gate lines” or “pixel selection lines”) which are formed in the direction which bridges one parallel side of an insulating substrate which generally forms a rectangular screen. Further, the liquid crystal display device also includes another insulating substrate which mounts a group of second electrodes (hereinafter also referred to as “data lines”, “source lines” or “drain lines”, “video signal lines”) thereon, wherein the group of second electrodes are formed in the direction which bridges another parallel side of the insulating substrate such that they cross the gate lines. Then, liquid crystal made of liquid crystal composition is sandwiched between the above insulating substrate and another insulating substrate thus constituting a liquid crystal panel.
The gate lines and the source lines are pulled out to end peripheries of the insulating substrate or are connected to leads provided to the end peripheries of the insulating substrate. Along the end periphery of the insulating substrate, a multi-layered printed circuit board is arranged and an electric connection between the leads and wiring formed on the multi-layered printed circuit board is established by printed circuit boards which connect the leads as a plurality of groups of leads or printed circuit boards for bridging which are referred to as tape carrier packages (TCP) or a chip-on-films (COF). Here, the tape-carrier-package TCP and the chip-on-film COF are printed circuit boards on which the semiconductor chips are mounted. Further, there exists another printed circuit board which directly mounts the semiconductor chips IC on end periphery of the insulating substrate. In this case, the connection between the insulating substrate and the wiring of the multi-layered printed circuit board is performed using a printed circuit board wiring simply. Such a connection is performed using solder or anisotropic conductive films ACF. Hereinafter, the explanation is made by mainly taking a case in which the above-mentioned connection is established using the tape carrier package TCP as an example.
Here, the modes of connection between the terminals of the gate lines and the source lines with the multi-layered printed circuit board are substantially equal and hence, the explanation is made only with respect to the mode for supplying signals at the source line side which constitutes the high density wiring hereinafter. The multi-layered printed circuit board includes laminated wiring consisting of a plurality of layers (for example, 6 to 10 layers) and transmits display data and timing signals such as a line clock signal (line pulse or referred to as CL1 in general), a pixel clock signal (a pixel pulse or a dot clock, CL2 in general), a frame clock signal (a frame pulse, referred to as CL3 in general) which are inputted from an external signal source (a host computer, a video signal generating circuit or the like) and supplies these signals to lead terminals of the source lines via the above-mentioned carrier tape packages TCP which mount leads of source lines as a group of plurality of lines on an insulating substrate. As literatures which disclose the constitution of the liquid crystal display device, JP-A-60-70601 and JP-B-51-13666 are named.